app:lint hangs after I upgraded the gradle plugin to 2.3.0.
Unexpected failure during lint analysis (this is a bug in lint or one of the libraries it depends on)
It complains about ProblemReporter.isClassPathCorrect(ProblemReporter.java:4761) and other places in ProblemReporter, but I was not able to pinpoint the problem.
Turns out this is caused by libraries that uses old lint APIs, in my case Timber and Butterknife. Once I updated those dependencies, lint finishes.
Thanks Josh Burton for sharing his solution with me!